The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2000-314651, filed on Oct. 16, 2000, the contents of which is herein expressly incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a battery module, and more particularly to a battery module made by connecting a plurality of recharge able batteries.
2. Description of Related Art
FIG. 6 shows a conventional battery module made by connecting a plurality of cells and coupling them integrally so as to obtain a necessary power capacity. In this battery module, a plurality of cells 31 (31a to 31e) made of sealed alkaline recharge able batteries as shown in FIG. 7 are arranged in a row with the long side walls of the prismatic cell cases 32 adjacent with each other. End plates 42 are placed against the outsides of the cell cases 32 of the cells 31a and 31e at the opposite ends, and the cells, together with the two end plates 42, 42, are bound together with binding strips 43, whereby the plurality of cells are coupled integrally.
The cell 31 is constituted by accommodating an electrode plate group 33 in the cell case 32 together with an electrolyte, and the opening of the cell case 32 is closed with a lid 35 provided with a safety vent 34. The electrode plate group 33 is formed by superimposing a positive electrode plate and a negative electrode plate with a separator interposed between them. From the upper end of the positive electrode plates on one side of the electrode plate group 33, leads 36 are drawn out upward and are connected to a positive electrode terminal 37 there above, and from the upper end of the negative electrode plates on the other side of the electrode plate group, leads 36 are drawn out upward and are connected to a negative electrode terminal 38 there above. The positive electrode terminal 37 and the negative electrode terminal 38 are attached to the lid 35.
In the battery module, the cells 31 are electrically connected in series, by connecting the positive electrode terminals 37 and the negative electrode terminals 38 of neighboring cells 31 with connection plates 41. When the cell cases 32 are coupled, ribs 39 which protrude vertically from the long side walls of the cell cases 32 abut against each other, so as to form a coolant passage 40 parallel to the vertical direction of the cell case 32. The coolant passage 40 is ventilated to cool each of the cells 31a to 31e. 
However, this conventional battery module has a problem that the connection path between the cells 31 is long, and a large number of connecting components are required since the connection between the cells 31 is affected such that the leads 36, which extend upward from the electrode plates, are connected to the electrode terminals 37 and 38 attached to the lid 35, and the terminals 37 and 38 are connected with the connection plate 41. Consequently, in this battery module, the component resistance caused by the components is large, and the ratio of the component resistance to the reactive resistance caused by the cell reaction between the positive and negative electrode plates and the electrolyte reaches as high as 40:60 to 50:50. This results in intense heat generation in the battery, preventing the battery module from achieving higher power output and improved service life characteristics.
Moreover, the battery module requires a large number of connecting components due to the complicated construction of the connection between the cells, so that the costs are high. Furthermore, the battery module occupies a relatively large space since the connection portions are exposed to the outside and a space above the cell case 32 is thus required.
In the light of these problems of the prior art, an object of the present invention is to provide a battery module in which the internal resistance per cell is reduced, and higher power output is achieved.
A battery module of the invention includes a plurality of cells having cell cases that accommodate an electrode plate group and an electrolyte; and an integrated battery case which accommodates the plurality of cells. According to the invention, the ratio of the component resistance per cell including the connecting resistance between the cells, to the reactive resistance in the cell caused by the cell reaction between the electrode plate group and the electrolyte, is made in the range of 1:99-40:60 at a temperature of 25xc2x0 C. Although the reactive resistance in the battery is difficult to reduce, the internal resistance per cell is reduced due to the reduction of the component resistance which is achieved by employing the integrated battery case for accommodating the plurality of cells. Thereby, heat generation in the battery is reduced, higher power output is achieved, and service life characteristics are improved.
The integrated battery case is rectangular shaped, made by coupling together a plurality of prismatic cell cases in line. The electrode plate group is formed by superimposing rectangular shaped positive and negative electrode plates with a separator interposed therebetween. Lead portions of the positive and negative electrode plates protrude to the sides opposite to each other, and the lead portions of the positive and negative electrode plates of adjacent cells are connected within the integrated battery case. The distance of the electric current route from the positive and negative electrode plates to their lead portions are thus shortened, and the electric current route between the adjacent cells is shortened as well, whereby the internal resistance of the battery module is reduced.
Preferably, collector plates are arranged on both sides of the electrode plate group and are welded to the lead portions of the positive and negative electrode plates respectively, whereby adjacent cells are electrically connected within the integrated battery case by connecting the positive and negative collector plates of the cells. The connecting resistance is reduced because the lead portion of each of the electrode plates is connected to the collector plate, and the connecting resistance between the cells is also reduced because the collector plates of In adjacent cells are connected within the integrated battery case.